It is well known that the alignment of the optical components is decisive for the quality of the devices that are fitted with the components. Therefore, any self-alignment, i.e. any assembly in which the properties of the output luminous flux are little sensitive to the orientation or to the position of one or several components, is required.
Among the self-aligned retroreflecting systems known for a long time, the following can be mentioned for exemplification purposes: the cube corner illustrated on FIG. 1 with which an incident beam 1, 1' on a reflecting orthogonal trihedron 3 produces a parallel output beam 2, 2', whatever the angle of incidence with respect to the diagonal 5 of the cube and the position of the point of incidence 4.
The so-called `cat's eye` assembly is also well known, consisting of a convergent optical system 8 with optical axis 9, in the focal plane of which is located a mirror 10, substantially perpendicular to the axis 9. A collimated incident beam 11, 11' converges onto the mirror 10, is reflected on the mirror 10 and then diverges in return onto the optical system 8 that produces an output beam 12, 12', also collimated and parallel to 11. Such a cat's eye is represented on FIG. 2.
Both these systems described previously offer self-alignment of the direction of the output beam 2, 2' and 12, 12' on the input beam, respectively 1, 1' and 11, 11' in two dimensions, i.e. in all the planes parallel to the direction of the input beams. In certain systems, one can seek to obtain the self-alignment in a single dimension. In this case, one can use either an orthogonal dihedron instead of the trihedron of FIG. 1 or a cylindrical cat's eye, i.e. a lens or a cylindrical optical system instead of the spherical optical system 8 in the case of FIG. 2. The dihedron ensures self-alignment in the plane perpendicular to its edge and the cylindrical cat's eye in the plane perpendicular to the generatrix of its cylindrical lens. In the parallel plane, both these systems behave like a mirror.
Self-aligned separating optical components or devices, which produce two emerging beams, parallel to one another, from a single incident beam, are also known. These may be for instance a periscope or a blade with parallel faces one of which is partially metallized, in order to modify its reflection coefficient on a portion of its surface.
Conventional dihedra and trihedra allow however only total reflection of the beam whereas, in certain applications, a second partial output is required in addition to the first retroreflected output.